This project is composed of two aspects; determination of the ovarian cell type which is the most sensitive to the action of the toxicant, i.e., the target cell, and then the determination of the mechanism of action of the toxicant on that particular cell. With regard to the first part, we have determined the ovarian target cell for cyclophosphamide (growing granulosa cells) and the target cell for phthalate esters (mature granulosa cells). Mechanistically we are examining the effect of phthalate esters on granulosa cell function (the target cell based on preliminary evidence) using granulosa cells cultured from DES-implanted immature rats (F-344). Mono(2-ethylhexyl)phthalate, the active metabolite of the phthalate ester di-(ethylhexyl)phthalate, inhibits FSH-stimulated cAMP accumulation in a time- and dose-dependent manner. MEHP also inhibits progesterone production and estradiol production. In granulosa cells MEHP, in addition to decreasing cAMP accumulation via an affect on FSH receptor coupling, has a specific action to inhibit aromatose activity. In vivo this inhibition of aromatose results in decreased estradiol and a lack of ovulation.